1. Field of the Disclosure
The present disclosure relates generally to ejection devices for printers, and more particularly, to methods for fabricating planar heater structures of the ejection devices.
2. Description of the Related Art
Fabrication of a typical ejection device (printhead) for a printer, such as an inkjet printer, involves fabrication of a heater structure (heater stack) using a substrate wafer, such as a silicon-based substrate wafer. Specifically, the substrate wafer may be used for arranging one or more fluid ejection elements (resistor elements/heat resistors) thereupon and for configuring a flow feature layer and a nozzle plate over the substrate wafer. Further, a drive circuitry layer made by complementary metal-oxide-semiconductor (CMOS) implantation may be used over the substrate wafer in order to electrically connect the ejection device to the printer during use.
Various backend and frontend processes have been employed for fabricating heater structures of ejection devices. Specifically, CMOS backend process is one such technique used for fabricating heater structures. Further, various layers (such as metallic layers and the like) may be used with a substrate wafer in a CMOS backend process and the surface of the substrate wafer may then be planarized using a chemical mechanical polishing (CMP) technique. However, the existing CMOS backend processes are incapable of completely/efficiently using the advantage of frontend CMP technique.
Further, with evolving technologies in the domain of ejection devices, heater structures with planar surfaces are being desired to be employed in order to increase efficiency of the ejection devices. Accordingly, for best utilization of such evolving technologies, CMP technique in backend processes may be a desired option to avail. Specifically, the CMP technique allows for planarization of a wafer surface. Accordingly, with CMP backend processes, surface topology of heater chips of any ejection device may be significantly improved. Such surface topology improvement may assist in overcoming current topography related issues associated with photo-imageable nozzle plate and fluid bottle assembly. In addition, fewer process steps may be required to achieve the desired surface topology as compared with existing processes. Moreover, CMP backend processes may assist in improving glass nozzle plate process margin and/or other nozzle technologies, and to enable other Micro-Electro-Mechanical Systems (MEMS) backend processes.
In general, CMP technique is traditionally performed on a material, such as silicon oxide and tungsten, for yielding planar heater structures from substrate wafers. However, other materials may be polished given the right choice of slurry employed for the CMP technique, and/or chemical and mechanical agents, to aid in polishing. For example, the choice of Methylsilsesquioxane (MSQ) in heater structures is made for insulative properties to aid in a more efficient thermal transfer for a fluid (ink) within ejection devices. Though, polishing of MSQ by the CMP technique is a slow process, and sometimes prone to defects, however, there exist appropriate slurries and compatible CMP methods that may effectively be used. Another material similar to MSQ is spin-on-glass (SOG) material. A CMP technique may also be carried out while using aluminum due to the simplicity of patterning of aluminum into any desired design. However, patterning aluminum by the CMP technique is problematic, as aluminum is a soft metal and is prone to smearing, dishing and other such defects.
Accordingly, there still persists a need for efficient and effective methods for fabricating planar heater structures by employing CMP backend processes, while overcoming the aforementioned disadvantages.